Xylene isomerization with a reactivated zeolite

ABSTRACT

A process is provided for converting feedstock comprising aromatic compounds to product comprising aromatic compounds which differs from the feedstock over catalyst prepared by a method for reactivating a catalyst composition comprising a crystalline zeolite material having a silicon/aluminum atomic ratio of at least about 2, said catalyst composition having been deactivated by contact with steam. The catalyst preparation method involves contacting said steam-deactivated catalyst composition with an aluminum compound at elevated temperature, and contacting said aluminum compound contacted catalyst composition with an aqueous acid solution.

CROSS REFERENCE

This is a continuation-in-part of application Ser. No. 608,737, filedMay 10, 1984 now abandoned, which is a division of application Ser. No.458,398, filed Jan. 17, 1983, and issued as U.S. Pat. No. 4,461,845, theentire contents thereof being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to use of a catalyst composition resulting from amethod for reactivating certain catalyst compositions comprisingcrystalline materials which have been steam-deactivated, said methodinvolving contact with an aluminum compound followed by controlledtreatment with an acid solution. In particular, this invention relatesto conversion of feedstock comprising aromatic compounds to productcomprising aromatic compounds which differs from the feedstock over sucha catalyst composition.

2. Description of the Invention

Zeolitic materials, both natural and synthetic, have been demonstratedin the past to have catalytic properties for various types ofhydrocarbon conversion. Certain zeolitic materials are ordered, porouscrystalline aluminosilicates having a definite crystalline structure asdetermined by X-ray diffraction, within which there are a large numberof smaller cavities which may be interconnected by a number of stillsmaller channels or pores. These cavities and pores are uniform in sizewithin a specific zeolitic material. Since the dimensions of these poresare such as to accept for adsorption molecules of certain dimensionswhile rejecting those of larger dimensions, these materials have come tobe known as "molecular sieves" and are utilized in a variety of ways totake advantage of these properties.

Such molecular sieves, both natural and synthetic, include a widevariety of positive ion-containing crystalline aluminosilicates. Thesealuminosilicates can be described as a rigid three-dimensional frameworkof SiO₄ and AlO₄ in which the tetrahedra are cross-linked by the sharingof oxygen atoms whereby the ratio of the total aluminum and siliconatoms to oxygen atoms is 1:2. The electrovalence of the tetrahedracontaining aluminum is balanced by the inclusion in the crystal of acation, for example an alkali metal or an alkaline earth metal cation.This can be expressed wherein the ratio of aluminum to the number ofvarious cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. Onetype of cation may be exchanged either entirely or partially withanother type of cation utilizing ion exchange techniques in aconventional manner. By means of such cation exchange, it has beenpossible to vary the properties of a given aluminosilicate by suitableselection of the cation. The spaces between the tetrahedra are occupiedby molecules of water prior to dehydration.

Prior art techniques have resulted in the formation of a great varietyof synthetic zeolites. The zeolites have come to be designated by letteror other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No.2,882,243), zeolite X (U.S. Pat. No. 2,882,244), zeolite Y (U.S. Pat.No. 3,130,007), zeolite ZK-5 (U.S. Pat. No. 3,247,195), zeolite ZK-4(U.S. Pat. No. 3,314,752), zeolite ZSM-5 (U.S. Pat. No. 3,702,886),zeolite ZSM-11 (U.S. Pat. No. 3,709,979), zeolite ZSM-12 (U.S. Pat. No.3,832,449), zeolite ZSM-20 (U.S. Pat. No. 3,972,983), ZSM-35 (U.S. Pat.No. 4,016,245), ZSM-38 (U.S. Pat. No. 4,046,859), and zeolite ZSM-23(U.S. Pat. No. 4,076,842), merely to name a few.

The silicon/aluminum atomic ratio of a given zeolite is often variable.For example, zeolite X can be synthesized with silicon/aluminum atomicratios of from 1 to 1.5; zeolite Y, from 1.5 to about 3. In somezeolites, the upper limit of the silicon/aluminum atomic ratio isunbounded. ZSM-5 is one such example wherein the silicon/aluminum atomicratio is at least 2.5 and up to infinity. U.S. Pat. No. 3,941,871 (U.S.Pat. No. Re. 29,948) discloses a porous crystalline silicate made from areaction mixture containing no deliberately added aluminum in the recipeand exhibiting the X-ray diffraction pattern characteristic of ZSM-5type zeolites. U.S. Pat. Nos. 4,061,724, 4,073,865 and 4,104,294describe crystalline silicas of varying aluminum and metal content.

The reactivation of steam-deactivated catalysts comprising such zeoliteshas been a prime objective of the petrochemical and refining industries.In contrast to coke-deactivated catalysts which can be readilyregenerated by air oxidation, no adequate technique has been heretoforedeveloped for reactivation of steam-deactivated catalysts. Steamdeactivation apparently involves removal of aluminum from zeoliticframework, a result which until now has been believed to be largelyirreversible.

It is noted that U.S. Pat. Nos. 3,354,078 and 3,644,220 relate totreating crystalline aluminosilicates with volatile metal halides,including aluminum chloride. Neither of these latter patents is,however, concerned with treatment of catalysts comprising zeolites,especially zeolites having initially a high silicon/aluminum atomicratio, which have been deactivated by contact with steam.

U.S. Pat. No. 4,354,049 teaches aromatization of C₂ -C₁₂ aliphatichydrocarbons in the vapor phase over catalyst comprising a zeolitehaving a SiO₂ /Al₂ O₃ molar ratio of greater than 12/1 which has beenexchanged or impregnated with aluminum.

U.S. Pat. No. 4,380,685 teaches para-selective alkylation,transalkylation or disproportionation of a substituted aromatic compoundto form a dialkylbenzene compound mixture over catalyst comprisingzeolite characterized by a Constraint Index of 1 to 12 and asilica:alumina mole ratio of at least 12:1, the catalyst having thereonincorporated various metals and phosphorus. Other patents coveringalkylation and transalkylation include U.S. Pat. Nos. 4,127,616,4,361,713, 4,365,104, 4,367,359, 4,370,508 and 4,384,155. Toluene isconverted to para-xylene in U.S. Pat. Nos. 3,965,207, 3,965,208,3,965,209, 4,001,346, 4,002,698, 4,067,920, 4,100,215 and 4,152,365, toname a few. Alkylation with olefins is taught, for example, in U.S. Pat.Nos. 3,962,364 and 4,016,218 and toluene is disproportionated in, forexample, U.S. Pat. Nos. 4,052,476, 4,007,231, 4,011,276, 4,016,219 and4,029,716. Isomerization of xylenes is taught in, for example, U.S. Pat.Nos. 4,100,214, 4,101,595, 4,158,676, 4,159,282, 4,351,979, 4,101,597,4,159,283, 4,152,363, 4,163,028, 4,188,282 and 4,224,141.

SUMMARY OF THE INVENTION

The present invention relates to a novel process for convertingaromatics. The process uses catalyst compositions comprising crystallinezeolites having a silicon/aluminum atomic ratio of at least 2,especially those zeolites having a silicon/aluminum atomic ratios ofgreater than 10, such as, for example, greater than 50, which have beendeactivated by contact with steam. The catalyst for use herein isprepared by the steps of contacting said steam-deactivated catalystcomposition with an aluminum compound, such as, for example, aluminumhalide, e.g. aluminum chloride, at an elevated temperature, followed bycontacting said catalyst composition with an aqueous acid solution, suchas, for example, an acid solution having a pH of less than about 5, e.g.less than about 2. The resulting reactivated catalyst compositionexhibits enhanced Bronsted acidity and, therefore, improved acidcatalytic activity.

EMBODIMENTS

This invention is concerned with the treatment of catalysts comprisingcrystalline material having a silicon/aluminum atomic ratio of at least2, especially those crystalline materials having high silicon/aluminumatomic ratios of greater than 10, such as, for example, greater than 50,which have been steam-deactivated. The expression "high siliconcrystalline material" is intended to define a crystalline structurewhich has a silicon/aluminum atomic ratio greater than about 10, morepreferably greater than about 50, still more preferably greater thanabout 100, up to and including those highly siliceous materials wherethe silicon/aluminum atomic ratio is as reasonably close to infinity aspractically possible. This latter group of high silicon crystallinematerials is exemplified by U.S. Pat. Nos. 3,941,871; 4,061,724;4,073,865 and 4,104,294 wherein the materials are prepared from reactionsolutions which involve no deliberate addition of aluminum. Smallquantities of aluminum are usually present in reaction solutions fromwhich high silicon crystalline material is to be synthesized. It is tobe understood that the expression "high silicon crystalline material"also specifically includes those materials which have other metalsbesides silicon and/or aluminum associated therewith, such as boron,iron, chromium, etc.

The catalyst preparation method is simple and easy to carry out althoughthe results therefrom are unexpected and dramatic. The first necessarystep of the method involves contacting a steam-deactivated catalystcomposition comprising crystalline zeolite material, said zeolitematerial having a silicon/aluminum atomic ratio of at least about 2,with an aluminum compound, such as the halide, e.g. fluoride, chlorideor bromide, at a temperature of from about 100° C. to about 850° C.,preferably from about 100° C. to about 500° C. The second necessary stepof the method involves contacting the aluminum compound contactedcomposition with an aqueous acid solution of from about 0.001 M to about10 M, preferably from about 0.1 M to about 2 M, at a temperature of fromabout 20° C. to about 100° C.

Certain optional steps may be employed to tailor reactivation ofsteam-deactivated catalyst for use herein. The first optional stepinvolves hydrolyzing the product catalyst from the above first necessarystep. This may be accomplished by contact of the first necessary stepproduct with, for example, water at a temperatuare of from about 20° C.to about 550° C. When the optional hydrolyzing step temperature is below100° C. at atmospheric pressure, liquid water may be used. When theboiling point of water is exceeded, such as when the optionalhydrolyzing step temperature exceeds 100° C. at atmospheric pressure,the catalyst product of the first necessary step may be purged withwater saturated gas, e.g. helium.

Another optional step involves calcining the product catalyst from theabove first necessary step or, if hydrolysis has been conducted as afirst optional step as above indicated, the product of said optionalhydrolysis step. This optional calcination step may be conducted at atemperature of from about 200° C. to about 600° C. in an inertatmosphere of air, nitrogen, etc. at subatmospheric, atmospheric orsuperatmospheric pressure for from about 1 minute to about 48 hours.

A further optional step involves calcining the product catalyst from theabove second necessary step at a temperature of from about 200° C. toabout 600° C. in an inert atmosphere of air, nitrogen, etc. atsubatmospheric, atmospheric or superatmospheric pressure for from about1 minute to about 48 hours.

During the first necessary step of contacting the steam-deactivatedcatalyst composition with an aluminum compound, said aluminum compoundmay be in vapor or liquid phase at the contacting temperature of fromabout 100° C. to about 850° C. By liquid phase, it is contemplated thatthe aluminum compound may be a melt or in aqueous or organic solution atthe contacting temperature.

The aluminum compound contacting step (first necessary) may beaccomplished in the vapor phase by admixture of the aluminum compoundvapor with an inert gas such as nitrogen or helium at a temperature offrom about 100° C. to about 850° C., preferably from about 100° C. toabout 500° C. The amount of aluminum compound vapor which is utilized isnot narrowly critical but usually from about 0.2 to about 2 grams ofaluminum compound are used per gram of crystalline material in thecatalyst composition. The aluminum compound may be an aluminum halidesuch as, for example, aluminum chloride.

The second necessary step of the method has been found to be critical inregenerating a catalyst composition comprising a crystalline zeolitematerial which has been deactivated by steam contact. In fact, when asteam-deactivated catalyst composition comprising a crystallinematerial, i.e. a high silicon crystalline zeolite, is contacted with analuminum compound, i.e. aluminum chloride vapor, hydrolyzed and calcinedunder indicated conditions, no significant activity enhancement isobserved. When the above steps are followed by contact with an aqueousacid solution, i.e. 1 M hydrochloric acid solution at appropriatecoanditions, e.g. 75° C., and thereafter calcined as indicated, adramatic increase in acid activity of the previously steam-deactivatedmaterial occurs.

The present process includes converting feedstock comprising aromaticcompounds selected from the group consisting of benzene and monocyclicalkyl-substituted benzene of from 7 to 10 carbon atoms to productcomprising aromatic compounds which differs from said feedstock,examples of which include isomerizing xylene feedstock components toproduct enriched in p-xylene with reaction conditions including atemperature from about 230° C. to about 510° C., a pressure of fromabout 3 atmospheres to about 35 atmospheres, a weight hourly spacevelocity of from about 0.1 hr⁻¹ to about 200 hr⁻¹ and ahydrogen/hydrocarbon mole ratio of from 0 (no added hydrogen) to about100; disproportionating toluene to product comprising benzene andxylenes with reaction conditions including a temperature of from about200° C. to about 760° C., a pressure of from about atmospheric to about60 atmospheres and a weight hourly space velocity of from about 0.08hr⁻¹ to about 20 hr⁻¹ ; alkylating aromatic hydrocarbons, e.g. benzeneand C₇ and C₈ alkylbenzenes, in the presence of an alkylating agent,e.g. olefins, formaldehyde, alkyl halides and alcohols, with reactionconditions including a temperature of from about 340° C. to about 500°C., a pressure of from about atmospheric to about 200 atmospheres, aweight hourly space velocity of from about 2 hr⁻¹ to about 2000 hr⁻¹ andan aromatic hydrocarbon/alkylating agent mole ratio of from about 1/1 toabout 20/1; and transalkylating aromatic hydrocarbons in the presence ofpolyalkylaromatic hydrocarbons with reaction conditions including atemperature of from about 340° C. to about 500° C., a pressure of fromabout atmospheric to about 200 atmospheres, a weight hourly spacevelocity of from about 10 hr⁻¹ to about 1000 hr⁻¹ and an aromatichydrocarbon/polyalkylaromatic hydrocarbon mole ratio of from about 1/1to about 16/1.

Reaction conditions for the conversion of aromatics as above-detailedinclude, in general, a temperature of from about 200° C. to about 760°C., a pressure of from about atmospheric to about 200 atmospheres, aweight hourly space velocity of from about 0.08 hr⁻¹ to about 2000 hr⁻¹,and a hydrogen/feedstock aromatic hydrocarbon mole ratio of from 0 (noadded hydrogen) to about 100.

Feedstock aromatic compounds converted hereby include individually andin mixture benzene and monocyclic alkyl-substituted benzene of from 7 to10 carbon atoms having the structure ##STR1## wherein R is methyl, ethylor a combination thereof, and n is an integer of from 1 to 4. In otherwords, the feedstock aromatic compounds may be benzene, benzenecontaininq from 1 to 4 methyl and/or ethyl group substituents, andmixtures thereof. Non-limiting examples of such feedstock compoundsinclude benzene, toluene, xylene, ethylbenzene, mesitylene(1,3,5-trimethylbenzene), durene (1,2,4,5-tetramethylbenzene),pseudocumene (1,2,4-trimethylbenzene) and mixtures thereof.

Other reactant species may be present, such as for alkylation.Alkylating agent species include olefins such as ethylene, propylene,dodecylene, as well as formaldehyde, alkyl halides and alcohols; thealkyl portion thereof having from 1 to 24 carbon atoms. Numerous otheracyclic compounds having at least one reactive alkyl radical may beutilized as alkylating agents.

Products of the present conversion process include alkyl-substitutedbenzene compounds which differ from feedstock compounds depending uponthe conversion desired. The following listing presents non-limitingexamples:

                                      TABLE II                                    __________________________________________________________________________    EFFECTS OF Al:Zr CATALYST COMPONENT RATIOS: PROPLYENE DIMERIZATION                                  TOLUENE SOLVENT: 20 ml                                                        PROPYLENE: 25-27 g                                                            CATALYST: Cp.sub.2 ZrCl.sub.2 + methylaluminoxane                             TEMP.: 35-47° C.                                                       PRESSURE: Autogenic                                                           REACTION TIME: 2 hrs.                                                           WEIGHT % SELECTIVITY TO VARIOUS DIMERS                       Al:Zr            (NORMALIZED TO 100%)                                         ATOMIC                                                                              CONVERSION            2,3-DIMETHYL-      2,3-DIMETHYL-           EXPT. NO.                                                                            RATIO OF PROPYLENE, %                                                                          2-Me-1-PENTENE                                                                           1-BUTENE 2-Me-PENTANE                                                                            BUTANE                  __________________________________________________________________________     9.sup.(a)                                                                            8:1  90         95.8       1.3      1.0       0.4                     10.sup.(b)                                                                            16:1 90   est.  95.8       2.3      1.8       0.1                     11.sup.(c)                                                                           420:1 71         76         13       9         1                       __________________________________________________________________________     .sup.(a) Oligomer Composition: 97.6% C.sub.6, 2.4% C.sub.9, 0% C.sub.12       (weight %).                                                                   .sup.(b) Oligomer Composition: 95.8% C.sub.6, 4.2% C.sub.9, 0% C.sub.12       (weight %).                                                                   .sup.(c) Oligomer Composition: 30.3% C.sub.6, 22.9% C.sub.9, 23.1%            C.sub.12, 12.3% C.sub.15, 7.8% C.sub.18, 2.8% C.sub.21, 0.87% C.sub.24        (weight %).                                                              

Mechanisms of the present process may be isomerization, alkylation,transalkylation and disproportionation. Disproportionation is a specialcase of transalkylation in which the alkylatable aromatic compound andthe transalkylating agent is the same compound, for example, whentoluene serves as the doner and acceptor of the transferred methyl groupto produce benzene and xylene. Use of the term transalkylation includesthe special case of disproportionation.

Of the catalysts comprising crystalline zeolites having asilicon/aluminum atomic ratio of at least 2 which are advantageouslyreactivated after steam deactivation, those comprising zeolites ofintermediate or large pore structure are noted. Intermediate porestructure zeolites provide a selective constrained access to and egressfrom the intracrystalline free space by virtue of having an effectivepore size intermediate between the small pore Linde A and the large poreLinde X, i.e. the pore windows of the structure are of about a size suchas would be provided by 10-membered rings of silicon atomsinterconnected by oxygen atoms. It is to be understood, of course, thatthese rings are those formed by the regular disposition of thetetrahedra making up the anionic framework of the crystalline zeolite,the oxygen atoms themselves being bonded to the silicon (or aluminum,etc.) atoms at the centers of the tetrahedra. Intermediate porestructure zeolites freely sorb normal hexane while access in the largermolecules is constrained. It is sometimes possible to judge from a knowncrystal structure whether such constrained access exists. For example,if the only pore windows in a crystal are formed by 8-membered rings ofsilicon and aluminum atoms, then access by molecules of largercross-section than normal hexane is excluded.

A simple determination of "Constraint Index" as herein defined may bemade to determine degree of constrained access to molecules larger incross-section than normal paraffins, and thereby whether a particularzeolite is composed of large or intermediate pores. Constraint Index maybe determined by passing continuously a mixture of an equal weight ofnormal hexane and 3-methylpentane over a sample of zeolite atatmospheric pressure according to the following procedure. A sample ofthe zeolite, in the form of pellets or extrudate, is crushed to aparticle size about that of coarse sand and placed in a glass tube.Prior to testing, the zeolite is treated with a stream of air at 540° C.for at least 15 minutes. The zeolite is then flushed with helium and thetemperature is adjusted between 290° C. and 538° C. to give an overallconversion of between 10% and 60%. The mixture of hydrocarbons is passedat 1 liquid hourly space velocity (i.e. 1 volume of liquid hydrocarbonper volume of zeolite per hour) over the zeolite with a helium dilutionto give a helium to (total) hydrocarbon mole ratio of 4:1. After 20minutes on stream, a sample of the effluent is taken and analyzed, mostconveniently by gas chromotography, to determine the fraction remainingunchanged for each of the two hydrocarbons.

While the above experimental procedure will enable one to achieve thedesired overall conversion of 10 to 60% for most zeolite samples andrepresents preferred conditions, it may occasionally be necessary to usesomewhat more severe conditions for samples of very low activity, suchas those having an exceptionally high silicon/aluminum atomic ratio. Inthose instances, a temperature of up to about 538° C. and a liquidhourly space velocity of less than one, such as 0.1 or less, can beemployed in order to achieve a minimum total conversion of about 10%.

The "Constraint Index" is calculated as follows: ##EQU1##

The test for Constraint Index is described in U.S. Pat. No. 4,016,218,incorporated herein by reference for further details in the test.

The Constraint Index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Intermediate pore size zeolitesinclude those having a Constraint Index of from about 1 to 12. Largepore size zeolites generally include those having a Constraint Index ofless than about 1. Constraint Index (CI) values for some typicalmaterials are:

                                      TABLE IV                                    __________________________________________________________________________    OLIGOMERIZATION OF 1-HEXENE                                                                         TOLUENE (SOLVENT): 30 ml                                                      Me.sub.3 Al, 4 mmoles + H.sub.2 O, 5 mmoles                                   Cp.sub.2 ZrCl.sub.2 : VARIABLE                                                HEXENE: 400 mmoles                                                            TEMPERATURE: 40° C.                              EXPT.                                                                         NO. TIME                                                                              Cp.sub.2 Zr.sub.2 Cl.sub.2                                                          Al:Zn     1-HEXENE  WT % SELECTIVITY                            17554                                                                             HRS mmoles                                                                              ATOMIC RATIO                                                                            CONVERSION %                                                                            2-HEXENE                                                                             C.sub.7 H.sub.14                                                                  DIMER                                                                              TRIMER                                                                              TETRAMER              __________________________________________________________________________    16  1   2.0   2         13.3      8.2    4.3 87.5 1.0                             2                   34.6      5.9    2.1 88.6 3.5                         17  1   1.0   4         63.1      4.1    1.7 91.1 3.8                             2                   92.5      2.5    1.2 94.5 1.9                         18  1   0.5   8         80.8      4.7    1.8 88.3 5.2                         19  1    0.25 16        58.6      7.0    3.2 84.6 4.7   0.6                       2                   84.2      5.5    2.2 89.2 3.0   0.2                   __________________________________________________________________________

Zeolite ZSM-20 is described in U.S. Pat. No. 3,972,983, the entirecontents of which are incorporated herein by reference. Zeolite Beta isdescribed in U.S. Pat. No. 3,308,069, the entire contents of which areincorporated herein by reference.

Of the catalysts comprising high silicon crystalline materialsadvantageously treated in accordance herewith, steam-deactivatedcatalysts comprising zeolites ZSM-5 and ZSM-11 are particularly noted.ZSM-5 is described in U.S. Pat. No. 3,702,886 and U.S. Pat. No.Re.29,948, the entire contents of each being hereby incorporated byreference herein. ZSM-11 is described in U.S. Pat. No. 3,709,979, theentire teaching of which is incorporated herein by reference. Othercatalysts comprising high silicon crystalline materials advantageouslytreated in accordance herewith include steam-deactivated catalystscomprising ZSM-5/ZSM-11 intermediate (U.S. Pat. No. 4,229,424, theentire contents of which are incorporated herein by reference), ZSM-12(U.S. Pat. No. 3,832,449, the contents of which are incorporated hereinby reference), ZSM-23 (U.S. Pat. No. 4,076,842, the entire contents ofwhich are incorporated herein by reference), ZSM-35 (U.S. Pat. No.4,016,245, the entire contents of which are incorporated herein byreference), and ZSM-38 (U.S. Pat. No. 4,046,859, the entire contents ofwhich are incorporated herein by reference). ZSM-35 and ZSM- 38 aresynthetic ferrierite-type materials. Another such high siliconcrystalline material is ZSM-48, described in U.S. Pat. No. 4,375,573,the entire contents of which are incorporated herein by reference.

Catalysts comprising crystalline materials having varying amounts ofstructural aluminum as well as metals such as, for example, boron,chromium, iron, etc. are reactivated after steam deactivation by thepresent process regardless of what other materials or metals are presentin the crystal structure.

The catalyst comprising zeolite which has been steam-deactivated may becomposed of the crystalline zeolite alone or said zeolite and a matrixcomprising another material normally resistant to the temperature andother condition employed in a chemical conversion process. Such matrixmaterial is useful as a binder and imparts greater resistance to thecatalyst for the severe temperature, pressure and reactant feed streamvelocity conditions encountered in many processes, such as, for example,cracking.

Useful matrix materials include both synthetic and naturally occurringsubstances, as well as inorganic materials such as clay, silica and/ormetal oxides such as alumina. The latter may be either naturallyoccurring or in the form of gelatinous precipitates or gels includingmixtures of silica and metal oxides. Naturally occurring clays which canbe composited with the zeolite include those of the montmorillonite andkaolin families, which families include the sub-bentonites and thekaolines commonly known as Dixie, McNamee, Georgia and Florida clays orothers in which the main mineral constituent is halloysite, kaolinite,dickite, nacrite or anauxite. Such clays can be used in the raw state asoriginally mined or initially subjected to calcination, acid treatmentor chemical modification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as silica-alumina,silica-magnesia, silica-zirconia, silica-thoria, silica-beryllia, andsilica-titania, as well as ternary compositions, such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia. The matrix may be in the form of a cogel.The relative proportions of zeolite component and inorganic matrix, onan anhydrous basis, may vary widely with the zeolite content rangingfrom about 1 to about 99 percent by weight and more usually in the rangeof from about 5 to about 80 percent by weight of the dry composite.

In order to more fully illustrate the nature of the invention and themanner of practicing same, the following examples are presented. In theexamples, whenever Alpha Value is examined, it is noted that the AlphaValue is an approximate indication of the catalytic cracking activity ofthe catalyst compared to a standard catalyst and it gives the relativerate constant (rate of normal hexane conversion per volume of catalystper unit time). It is based on the activity of the highly activesilica-alumina cracking catalyst taken as an Alpha of 1 (RateConstant=0.016 sec⁻¹). In the case of zeolite HZSM-5, only 174 ppm oftetrahedrally coordinated Al₂ O₃ are required to provide an Alpha Valueof 1. The Alpha Test is described in U.S. Pat. No. 3,354,078 and in TheJournal of Catalysis, Vol. IV, pp. 527-529 (August 1965), eachincorporated herein by reference as to that description.

EXAMPLE 1

A high silicon crystalline material, i.e. zeolite ZSM-5 having asilicon/aluminum atomic ratio of about 42, was ammonium exchanged byrefluxing the calcined crystalline material in 1 M NH₄ Cl. Theammonium-exchanged ZSM-5 was then calcined for 60 minutes at 540° C. toprovide an acid form zeolite ZSM-5, i.e. HZSM-5. The Alpha Value of thisHZSM-5 was measured to be 190.

EXAMPLE 2

A first quantity of the high silicon crystalline zeolite product ofExample 1 was contacted with 100% steam at 538° C. for 22 hours in orderto damage, or deactivate, the zeolite. Examination of the Alpha Value ofthe steamed zeolite established severe deactivation. The Alpha Value wasreduced from the pre-steamed 190 value to only 16.

EXAMPLE 3

One-half of the steam-deactivated zeolite of Example 2 was placed in areactor vessel and contacted with 1M HCl solution for 3 hours at 75° C.The contacted zeolite was washed free of excess hydrochloric acidsolution and tested for Alpha Value. It proved to have an Alpha Value ofonly 15. There was no acid activation of the steam-deactivated highsilicon crystalline zeolite by the hydrochloric acid solutioncontacting.

EXAMPLE 4

The zeolite product of Example 3 was contacted with aluminum chloridevapor at 250° C. for 3 hours, and then heated to 500° C. for 1 hour. Thealuminum chloride vapor contacted material was then contacted with waterat 20° C. for 17 hours. The water contacted material was then calcinedat 538° C. in air for 10 hours and again tested for acid activity. ItsAlpha Value was only 15. There was no acid activation of thesteam-deactivated high silica crystalline zeolite by the steps ofhydrochloric acid solution contacting, followed by aluminum chloridevapor contacting, followed by hydrolysis and then calcination.

EXAMPLE 5

The product zeolite of Example 4 was then contacted with 1M HCl solutionfor 3 hours at 75° C. and calcined at 538° C. in air for 10 hours. TheAlpha Value of the zeolite was again tested. It was 41, a dramaticincrease not expected due to the results of Examples 3 and 4.

EXAMPLE 6

In order to obtain evidence establishing reactivation steps necessaryfor the present method, the second half of the steam-deactivated zeoliteof Example 2 was placed in a reactor vessel and contacted with aluminumchloride vapor at 250° C. for 2 hours, and then heated to 500° C. for 1hour. The aluminum chloride vapor contacted material was contacted withwater at 20° C. for 17 hours and then calcined at 538° C. in air for 10hours. The calcined material was then contacted with 1M HCl solution for3 hours at 75° C. and again calcined at 538° C. in air for 10 hours. TheAlpha Value of the product zeolite was measured to be 57. This was a 256percent increase in activity.

For further evidence of reactivation method step sequence and effect,the following experiments were conducted.

EXAMPLE 7

A second quantity of the high siliconcrystalline zeolite product ofExample 1 was contacted with 100% steam at 500° C. for 22 hours in orderto damage, or deactivate, the zeolite. The Alpha Value of the productzeolite was 29, establishing severe deactivation.

EXAMPLE 8

One-half of the steam-deactivated zeolite product of Example 7 wasplaced in a reactor vessel and contacted with 1M HCl solution for 3hours at 75° C. The hydrochloric acid solution contacted zeolite wascalcined at 538° C. for 10 hours and then tested in the Alpha Test. ItsAlpha Value was only 30.

EXAMPLE 9

The second half of the steam-deactivated zeolite product of Example 7was placed in a reactor vessel and treated by the sequential steps of(1) contacting said deactivated zeolite with aluminum chloride vapor at300° C. for 2 hours, and then heated to 500° C. for 1 hour, (2)contacting the step (1) product with water at 20° C. for 17 hours, (3)calcining the step (2) product at 538° C. The Alpha Value of the finalproduct zeolite was measured to be 123. This was a 324 percent increasein activity.

EXAMPLE 10

A high silicon crystalline material, i.e. zeolite ZSM-5 having asilicon/aluminum atomic ratio of about 35, was ammonium exchanged as inExample 1, combined with 35 wt. % alumina matrix and extruded intoextrudate particles (65 wt. % ZSM-5, 35 wt. % alumina). The extrudateproduct was calcined for 60 minutes in air at 538° C. to provide HZSM-5extrudate established to have an Alpha Value of about 200.

EXAMPLE 11

The extrudate of Example 10 was contacted with 1 atmosphere steam at600° C. for 2 hours. The Alpha Value of this steam damaged, ordeactivated, zeolite extrudate was established to be only 14.

EXAMPLE 12

The steam deactivated extrudate of Example 11 was washed with 0.1 Msodium hydroxide solution to convert same to sodium form, then contactedwith aluminum chloride vapor at 150° C. to 500° C. while heating at 2°C./minute, then contacted with water at 20° C. for 2 hours and thencalcined at 538° C. in air for 10 hours. The extrudate treated in thismanner was then tested for Alpha activity. Its Alpha Value was only 13.

EXAMPLE 13

The product extrudate of Example 12 was contacted with 1M hydrochloricacid solution at 75° C. for 3 hours and then calcined in air at 538° C.for 10 hours. The Alpha Value of the product of this example wasestablished to be 78, a 457 percent increase from the value of 14obtained for the steam-deactivated extrudate material of Example 11.

The following experiments were conducted to further establish effect ofthe present method upon steam-deactivated catalyst comprising a zeoliteand a matrix.

EXAMPLE 14

A high silicon crystalline material, i.e. zeolite ZSM-5 having asilicon/aluminum atomic ratio of about 35, was ammonium exchanged as inExample 10 and then extruded with alumina binder to yield extrudateparticles composed of 65 weight percent zeolite and 35 weight percentalumina.

EXAMPLE 15

The extrudate catalyst of Example 14 was steamed (100% steam) for 16hours at 454° C. Its Alpha Value was measured to be about 70. It wasfurther steamed (100% steam) at 538° C. for 22 hours. Its Alpha Valuewas then measured to be only 14.

EXAMPLE 16

The steam-deactivated catalyst extrudate of Example 15 (Alpha Value of14) was placed in a reactor vessel and treated by the sequential stepsof (1) contacting said deactivated extrudate catalyst with aluminumchloride vapor at 300° C. for 2 hours and then at 500° C. for 1 hour,(2) contacting the step (1) product with water at 20° C. for 17 hours,(3) calcining the step (2) product at 538° C. in air for 10 hours, (4)contacting the step (3) product with 1M HCl solution for 3 hours at 75°C., and (5) calcining the step (4) product in air for 10 hours at 538°C. The Alpha Value of the final product catalyst extrudate was measuredto be 78. This was a 457 percent increase in activity.

EXAMPLE 17

To exemplify operation of the present invention, a 2 gram quantity ofcalcined product from Example 16 is placed in a reactor vessel andcontacted with a feedstock comprised of 80% m-xylene and 20%ethylbenzene in the presence of added hydrogen at a ratio ofhydrogen/hydrocarbons of 6.5/1. At reaction conditions including atemperature of 428° C., 58.5 WHSV (hr⁻ 1) and a pressure of 10.2atmospheres, approximately 52% of the m-xylene and 51% of theethylbenzene are converted. The product is comprised as follows, valuesapproximate:

    ______________________________________                                        Product Component Wt. %                                                       ______________________________________                                        Benzene           4                                                           Toluene           1                                                           Ethylbenzene      9                                                           p-Xylene          18                                                          m-Xylene          39                                                          o-Xylene          18                                                          Ethyltoluenes     1                                                           Trimethylbenzenes 3                                                           Other             7                                                           ______________________________________                                    

What is claimed is:
 1. A process for converting a feedstock comprisingxylene isomers to isomerization conversion product which comprisescontacting said feedstock at conversion conditions sufficient to convertsaid feedstock to said product with a catalyst composition comprising acrystalline zeolite material having a silicon/aluminum atomic ratio ofat least about 2, said catalyst composition having been deactivated bycontact with steam and reactivated by the steps ofcontacting saidsteam-deactivated catalyst composition with an aluminum compound vaporat a temperature of from about 100° C. to about 850° C., and thereaftercontacting said aluminum compound contacted catalyst composition with anaqueous acid solution of from about 0.001 molar to about 10 molar at atemperature of from about 20° C. to about 100° C.
 2. The process ofclaim 1 wherein said crystalline zeolite material has a silicon/aluminumatomic ratio greater than
 10. 3. The process of claim 1 wherein saidaqueous acid solution is from about 0.1 molar to about 2 molar.
 4. Theprocess of claim 1 wherein said aluminum compound is aluminum halide. 5.The process of claim 1 which comprises the additional step of calciningsaid acid solution contacted catalyst composition at a temperature offrom about 200° C. to about 600° C.
 6. The process of claim 5 whichcomprises the additional step of calcining said aluminum compoundcontacted catalyst composition at a temperature of from about 200° C. toabout 600° C. prior to said acid solution contacting step.
 7. Theprocess of claim 1 wherein said aluminum compound contacting steptemperature is from about 100° C. to about 500° C., and said aqueousacid solution is from about 0.1 molar to about 1 molar.
 8. The processof claim 1 wherein said crystalline zeolite material is selected fromthe group consisting of large pore structure zeolites exhibiting aConstraint Index of less than about 1 and intermediate pore structurezeolites exhibiting a Constraint Index of from about 1 to about
 12. 9.The process of claim 1 wherein said crystalline zeolite material isselected from the group consisting of those having the structures ofZSM-5, ZSM-11, ZSM-5/ZSM-11 intermediate, ZSM-12, ZSM-20, ZSM-23,ZSM-35, ZSM-38, ZSM-48, zeolite Y and zeolite Beta.
 10. The process ofclaim 1 wherein said catalyst composition is a composite of said zeolitematerial and a matrix.
 11. The process of claim 10 wherein said matrixis alumina.
 12. The process of claim 1 wherein said acid solution is anaqueous solution of hydrochloric acid.
 13. The process of claim 1wherein said conversion conditions include a temperature of from about230° C. to about 510° C., a pressure of from about 3 atmospheres toabout 35 atmospheres, a weight hourly space velocity of from about 0.1hr⁻¹ to about 200 hr⁻¹ and a hydrogen/feedstock hydrocarbon compoundmole ratio of from 0 to about 100.